This tunnel has already been mined and runs from Little Tokyo to 4th and Flower streets.

Los Angeles Mayor and Metro Board Chair Eric Garcetti today toured the new Little Tokyo/Arts District Station that is under construction as part of the Regional Connector project. A tunnel boring machine is being prepared to soon begin digging the second of the project’s twin 1.9-mile tunnels that will ultimately link the Blue, Expo and Gold Lines under downtown L.A.

Once complete, the project will create two light rail lines from the three existing lines: one line will run between Azusa and Long Beach and the other between East Los Angeles and Santa Monica.

The two lines will share five downtown L.A. stations and riders will benefit from faster, more frequent trips to and through downtown Los Angeles that require far fewer transfers. The project is forecast to be complete in 2021. Here’s the project home page which has tons more info about the Regional Connector.